The TinEye project is an image search engine that helps to find where your images are displayed in the web.
So if you're ever wondering where else but flickr are your photos 'travelling' around internet without your knowledge and permission (or just curious, how famous you already are ) try TinyEye.
For the time being it's in private beta version, so it means you need to be invited. But you can put yourself on invite demand list and you should be able to use it when they grant you an invitation.
I got my invitation after a day, so they're quite fast. I'm not yet allowed to give any invitation to anyone, but if I'll be able and someone wants it, tell me.
Of course it's a great utility not only to search if your works has been ripped, but also to find images you want when you search for some famous painting or anything you need. It's mainly the tool for searching similar pictures. So it's not only for copyright violations.